For example, a high-pressure piping part having therein a passage for passing high-pressure fuel to be supplied to an internal combustion engine is a constituent part for forming a body of an injector for a diesel engine.
Generally, in a case of manufacturing this piping part, because of convenience in terms of equipment, a billet 101 shaped like a circular column shown in FIG. 11A is forged in a radial direction in a half closed manner to form a forged body 102 as shown in FIG. 11B. Then, a flash (burr) 103 and the like are trimmed to form a body structure 110. Then, a passage for passing high-pressure fuel is formed in this body structure 110.
The fuel flowing through the passage of this injector body has a very high pressure (for example, pressure of 180 MPa) and hence a large degree of allowance is provided to the resistance to pressure of the injector body.
In recent years, in order to respond to a trend toward larger power and cleaner exhaust gas of a diesel engine, the pressure of fuel to be supplied has been desired to be further increased. However, it is difficult to further improve the resistance to pressure of the injector body of a high-pressure piping part manufactured by the above-mentioned manufacturing method in the related art. Hence, there is presented a problem that it is difficult to secure the same degree of allowance of the resistance to pressure as ever.